1. Field of the Invention
The present invention relates to a film supply apparatus for affixing a film to the surface of a container such as a bottle, can or the like.
2. Description of the Prior Art
The conventional method of affixing a heat-shrinkable plastic film strip (hereinafter referred to briefly as film) to the surface of a container with the intent of the film strip functioning as a label or as a label and protective film generally comprises cutting the film to size, lapping one of its ends on the other to form a tubing, sleeving it over the container and subjecting it to thermal shrinking treatment with a hot blast of air so as to bring the film into intimate contact with the container surface.
Recently, for purposes of simplying the process and increasing the productivity and so on, an alternative method has been proposed which is such that a film is directly wrapped around the container, the lapped ends welded to form a tubing, and the tubing subjected to thermal shrinking treatment. And as a means for use in the application of film to the container in such a process, the apparatus depicted in FIG. 5 was proposed (Japanese Patent Application No. 60-109982). Referring to FIG. 5, this apparatus includes a container transport table 100 and a film supply unit 110. The film supply unit 110 comprises a pair of rolls 111, 112, a belt 113 thrown on said rolls and driven at a predetermined speed, and a vacuum suction system (not shown) connected to said belt 113, a vacuum suction force for attracting the film acting on the surface of the belt 113. The film F paid out from a film roll 120 onto the surface of the belt 113 is cut to size by a cutter (not shown) disposed in an intermediate position therebetween, retained in position under suction on the belt 113 and further fed in the direction of the arrowmark as the belt is driven.
The container transport table 100 is a rotary disk element adapted to spin about its center axis at a constant speed (in the clockwise direction in the illustration) and a plurality of container holder bases 101 are disposed along its circumferential periphery at substantially equispaced intervals. Disposed on one side of each container holder base 101 is a sucker plate 130 which is driven in the vertical direction by a lift means (not shown) from a position juxtaposed to the lateral side of a container X set on said container holder base 101 to a position downwardly apart from said lateral side of the container or vice versa and is adapted to rotate around the container at a constant speed (in the counterclockwise direction in the illustration) in said position juxtaposed to the lateral side of the container.
The sucker plate 130 has two rows of vacuum suction holes 131, 132 discharging on its exterior surface, with the left (in the illustration) row of vacuum suction holes 132 being adapted to retain the leading edge (F1) of film F while the other row of vacuum suction holes 131 is adapted to retain the trailing edge (F2) of film F, both under suction. The vacuum suction force acting at these rows of vacuum suction holes 131, 132 is controlled ON and OFF in association with the rotation of the sucker plate 130.
The apparatus further includes a film pressure bonding unit (140) which is located behind a container X on the container holder base 101 and adapted to advance and retreat in the radial direction of the container transport table in association with the rotation of the table. The pressure bonding unit 140 includes a front pressor face portion 141 having a built-in heat source and, as described in detail hereinafter, presses and heat-welds the lapped leading and trailing edges of film F.
FIG. 6 [I] through [II] show the process of wrapping a container with film by means of the above apparatus. Wrapping starts at the position P1 and ends at the position P2. Thus, the rotation of the container transport table 100 causes the container X on the container holder base 101 to reach the wrapping start position P1 along with the sucker plate 130. At the same time, the film F paid out and retained under suction on the belt 113 of the film supply unit arrives at the vicinity of the container X and its leading edge F1 is severed from the belt 113 surface and sucked onto the surface of the row of vacuum suction holes 132 of the sucker plate 130 under the influence of the suction force acting at the holes 132 (FIG. 6 [I]). As the sucker plate revolves around the container X, the film F whose leading edge F1 is retained in position under suction on the sucker plate 130 is peeled off the belt 113 surface and wrapped around the container X. When the sucker plate 130 has substantially completed one revolution around the container X and reached the wrapping end position P2, the trailing edge F2 of film facing the sucker plate 130 is severed from the belt 113, sucked on the sucker plate 130 by the suction force acting in the row of vacuum suction holes 131 and lapped over the front part of the leading edge F1 which has already been sucked. This completes the wrapping process (FIG. 6 [II]).
When the film F has been wrapped around the container X, the sucker plate 130 carrying said leading and trailing edges F1, F2 of film F makes a one-half revolution and stops in the position juxtaposed to the film pressure bonding unit 140 behind the container. Then, the pressure bonding unit 140 advances toward the sucker plate 130 and its pressor face portion 141 presses the lapped part of leading and the trailing edges F1, F2 of film F to thereby weld (heat weld) the joint (FIG. 6 [III]). As this welding is completed, the sucker plate 130 stops delivering the vacuum suction force and is withdrawn downward from the position intermediate between the film F and container X. The film F wrapped around the container X is then subjected to thermal shrinkage treatment whereby it is shrink-fitted onto the surface of the container.
Thus, the wrapping of the container with film is effected by driving the sucker plate 130 around the container but since the container itself is also moving in association with the rotation of the transport table, the motion of the sucker plate 130 is the composition of the rotary motion of the sucker plate itself around the container and the motion of the container accompanying the rotation of the sucker plate. On the other hand, the supply of film to the sucker plate is done as a constant-speed linear motion by the travel of the belt 113. Therefore, during the film wrapping process, film F tends to slip on the surface of the sucker plate and on the surface of the belt. As the film slips, there occurs a vertical or lateral misalignment of the leading and trailing edges of film to be lapped so that the condition of film on the container and, hence, the market value of the product are adversely affected.
This slippage of film and the consequent wrapping defect occur also when the film is directly wrapped around the container by rotating the container about its own axis without the use of a sucker plate.